![Dave Hansen](/assets/img/avatar_default.png)
The arch-specific mm_context_t is a great place to put protection-key allocation state. But, we need to initialize the allocation state because pkey 0 is always "allocated". All of the runtime initialization of mm_context_t is done in *_ldt() manipulation functions. This renames the existing LDT functions like this: init_new_context() -> init_new_context_ldt() destroy_context() -> destroy_context_ldt() and makes init_new_context() and destroy_context() available for generic use. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave@sr71.net> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20160212210234.DB34FCC5@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
295 lines
6.4 KiB
C
295 lines
6.4 KiB
C
/*
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* Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
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* Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
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* Copyright (C) 2002 Andi Kleen
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*
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* This handles calls from both 32bit and 64bit mode.
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*/
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#include <linux/errno.h>
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#include <linux/gfp.h>
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#include <linux/sched.h>
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#include <linux/string.h>
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#include <linux/mm.h>
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#include <linux/smp.h>
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#include <linux/slab.h>
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#include <linux/vmalloc.h>
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#include <linux/uaccess.h>
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#include <asm/ldt.h>
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#include <asm/desc.h>
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#include <asm/mmu_context.h>
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#include <asm/syscalls.h>
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/* context.lock is held for us, so we don't need any locking. */
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static void flush_ldt(void *current_mm)
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{
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mm_context_t *pc;
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if (current->active_mm != current_mm)
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return;
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pc = ¤t->active_mm->context;
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set_ldt(pc->ldt->entries, pc->ldt->size);
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}
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/* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
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static struct ldt_struct *alloc_ldt_struct(int size)
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{
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struct ldt_struct *new_ldt;
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int alloc_size;
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if (size > LDT_ENTRIES)
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return NULL;
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new_ldt = kmalloc(sizeof(struct ldt_struct), GFP_KERNEL);
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if (!new_ldt)
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return NULL;
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BUILD_BUG_ON(LDT_ENTRY_SIZE != sizeof(struct desc_struct));
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alloc_size = size * LDT_ENTRY_SIZE;
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/*
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* Xen is very picky: it requires a page-aligned LDT that has no
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* trailing nonzero bytes in any page that contains LDT descriptors.
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* Keep it simple: zero the whole allocation and never allocate less
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* than PAGE_SIZE.
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*/
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if (alloc_size > PAGE_SIZE)
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new_ldt->entries = vzalloc(alloc_size);
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else
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new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL);
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if (!new_ldt->entries) {
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kfree(new_ldt);
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return NULL;
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}
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new_ldt->size = size;
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return new_ldt;
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}
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/* After calling this, the LDT is immutable. */
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static void finalize_ldt_struct(struct ldt_struct *ldt)
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{
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paravirt_alloc_ldt(ldt->entries, ldt->size);
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}
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/* context.lock is held */
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static void install_ldt(struct mm_struct *current_mm,
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struct ldt_struct *ldt)
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{
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/* Synchronizes with lockless_dereference in load_mm_ldt. */
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smp_store_release(¤t_mm->context.ldt, ldt);
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/* Activate the LDT for all CPUs using current_mm. */
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on_each_cpu_mask(mm_cpumask(current_mm), flush_ldt, current_mm, true);
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}
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static void free_ldt_struct(struct ldt_struct *ldt)
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{
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if (likely(!ldt))
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return;
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paravirt_free_ldt(ldt->entries, ldt->size);
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if (ldt->size * LDT_ENTRY_SIZE > PAGE_SIZE)
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vfree(ldt->entries);
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else
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free_page((unsigned long)ldt->entries);
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kfree(ldt);
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}
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/*
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* we do not have to muck with descriptors here, that is
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* done in switch_mm() as needed.
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*/
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int init_new_context_ldt(struct task_struct *tsk, struct mm_struct *mm)
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{
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struct ldt_struct *new_ldt;
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struct mm_struct *old_mm;
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int retval = 0;
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mutex_init(&mm->context.lock);
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old_mm = current->mm;
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if (!old_mm) {
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mm->context.ldt = NULL;
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return 0;
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}
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mutex_lock(&old_mm->context.lock);
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if (!old_mm->context.ldt) {
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mm->context.ldt = NULL;
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goto out_unlock;
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}
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new_ldt = alloc_ldt_struct(old_mm->context.ldt->size);
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if (!new_ldt) {
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retval = -ENOMEM;
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goto out_unlock;
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}
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memcpy(new_ldt->entries, old_mm->context.ldt->entries,
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new_ldt->size * LDT_ENTRY_SIZE);
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finalize_ldt_struct(new_ldt);
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mm->context.ldt = new_ldt;
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out_unlock:
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mutex_unlock(&old_mm->context.lock);
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return retval;
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}
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/*
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* No need to lock the MM as we are the last user
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*
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* 64bit: Don't touch the LDT register - we're already in the next thread.
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*/
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void destroy_context_ldt(struct mm_struct *mm)
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{
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free_ldt_struct(mm->context.ldt);
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mm->context.ldt = NULL;
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}
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static int read_ldt(void __user *ptr, unsigned long bytecount)
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{
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int retval;
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unsigned long size;
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struct mm_struct *mm = current->mm;
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mutex_lock(&mm->context.lock);
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if (!mm->context.ldt) {
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retval = 0;
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goto out_unlock;
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}
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if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
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bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
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size = mm->context.ldt->size * LDT_ENTRY_SIZE;
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if (size > bytecount)
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size = bytecount;
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if (copy_to_user(ptr, mm->context.ldt->entries, size)) {
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retval = -EFAULT;
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goto out_unlock;
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}
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if (size != bytecount) {
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/* Zero-fill the rest and pretend we read bytecount bytes. */
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if (clear_user(ptr + size, bytecount - size)) {
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retval = -EFAULT;
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goto out_unlock;
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}
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}
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retval = bytecount;
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out_unlock:
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mutex_unlock(&mm->context.lock);
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return retval;
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}
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static int read_default_ldt(void __user *ptr, unsigned long bytecount)
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{
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/* CHECKME: Can we use _one_ random number ? */
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#ifdef CONFIG_X86_32
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unsigned long size = 5 * sizeof(struct desc_struct);
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#else
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unsigned long size = 128;
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#endif
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if (bytecount > size)
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bytecount = size;
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if (clear_user(ptr, bytecount))
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return -EFAULT;
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return bytecount;
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}
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static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
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{
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struct mm_struct *mm = current->mm;
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struct desc_struct ldt;
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int error;
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struct user_desc ldt_info;
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int oldsize, newsize;
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struct ldt_struct *new_ldt, *old_ldt;
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error = -EINVAL;
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if (bytecount != sizeof(ldt_info))
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goto out;
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error = -EFAULT;
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if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
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goto out;
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error = -EINVAL;
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if (ldt_info.entry_number >= LDT_ENTRIES)
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goto out;
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if (ldt_info.contents == 3) {
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if (oldmode)
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goto out;
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if (ldt_info.seg_not_present == 0)
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goto out;
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}
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if ((oldmode && !ldt_info.base_addr && !ldt_info.limit) ||
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LDT_empty(&ldt_info)) {
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/* The user wants to clear the entry. */
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memset(&ldt, 0, sizeof(ldt));
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} else {
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if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
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error = -EINVAL;
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goto out;
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}
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fill_ldt(&ldt, &ldt_info);
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if (oldmode)
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ldt.avl = 0;
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}
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mutex_lock(&mm->context.lock);
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old_ldt = mm->context.ldt;
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oldsize = old_ldt ? old_ldt->size : 0;
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newsize = max((int)(ldt_info.entry_number + 1), oldsize);
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error = -ENOMEM;
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new_ldt = alloc_ldt_struct(newsize);
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if (!new_ldt)
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goto out_unlock;
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if (old_ldt)
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memcpy(new_ldt->entries, old_ldt->entries, oldsize * LDT_ENTRY_SIZE);
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new_ldt->entries[ldt_info.entry_number] = ldt;
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finalize_ldt_struct(new_ldt);
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install_ldt(mm, new_ldt);
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free_ldt_struct(old_ldt);
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error = 0;
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out_unlock:
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mutex_unlock(&mm->context.lock);
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out:
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return error;
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}
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asmlinkage int sys_modify_ldt(int func, void __user *ptr,
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unsigned long bytecount)
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{
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int ret = -ENOSYS;
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switch (func) {
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case 0:
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ret = read_ldt(ptr, bytecount);
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break;
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case 1:
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ret = write_ldt(ptr, bytecount, 1);
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break;
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case 2:
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ret = read_default_ldt(ptr, bytecount);
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break;
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case 0x11:
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ret = write_ldt(ptr, bytecount, 0);
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break;
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}
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return ret;
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}
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